A power expander being adapted of counting times of breast expanding, it comprises a first and a second handle, a slide seat, a plurality of elastic members and a counter, wherein the slide seat is connected to the first handle to be movable relatively within a limited range; one end of each of the elastic members is connected to a second handle, the other end is connected to the slide seat; the counting member is connected to the slide seat to contact an actuating member of the first handle. Thereby, when a user exerts force on the first and the second handle to stretch the elastic members, elastic members move the slide seat; the slide seat is moved relatively to the first handle, the actuating member contacts to press the counting member to do a counting action.